Modern inorganic chemistry

THE LANTHANIDES AND ACTINIDES 445

heavy' elements, well beyond this range, may also have nuclear

stability, but their synthesis remains as a formidable problem.

QUESTION

1. The lanthanides and actinides are two series of fourteen
   elements, the members of each series having very similar properties.
   How do you account for these similarities, and for the fact that all
   the elements are metals?